The present invention relates to an idling operation control apparatus for an internal combustion engine, more particularly to an idling operation control apparatus adapted to regulate fuel to be supplied for every cylinder so as to minimize the dispersion of the output from each cylinder of a multiple cylinder engine.
In the control of the amount of fuel injection of the multiple cylinder engine according to the prior art, the fuel injection amount is uniformly controlled for all the cylinders in common. Accordingly, the output from each of the cylinders was not equal due to differences within the manufacturing tolerance of the internal combustion engine and/or the fuel injection pump and the like.
In particular, non-uniform output of the cylinders causes striking degradation in the stability of the engine during the idling operation of the engine, and this in turn increases engine vibrations and the amount of harmful components included in the exhaust gas. In addition, disadvantages such as noise are generated by the vibration of the engine.
In order to overcome the above disadvantages, there have been proposed various apparatuses for respectively controlling the fuel to be injected into each cylinder of the engine according to an individual cylinder control system. Some examples of the apparatuses of the type are disclosed in U.S. Pat. No. 4,495,920 in which a target average engine speed value is calculated by sampling the engine speeds at an integer multiple of the number of cylinders and the control of the amount of fuel injection is carried out for each cylinder on the basis of the difference between the engine speed of each cylinder and the target value thus calculated, utilizing a "learning system."
In each of the control apparatuses according to the prior art, however, since the following fuel injection amount was predicted from the difference between the average engine speed and the instantaneous speed of each cylinder by the learning system, much time is required by the microprocessor in evaluating the result of the learning. As a result, the control response is not good. In addition, a complicated algorithm has been necessary in order to evaluate the result of the learning, thus creating the problem of many procedures being necessary for the development thereof.
Furthermore, it is necessary for such a control to detect the timing of the combustion stroke of each cylinder, and in the conventional device, the timing was detected on the basis of a signal from a sensor which electrically detects the timing of the opening of a fuel injection valve and a signal from a reference timing sensor mounted on the crankshaft of the engine.
However, the above-described construction renders detection of the timing of the fuel injection impossible and appropriate control cannot be continued if the crankshaft sensor malfunctions. As a result, in this case, the individual cylinder control system causes instability in the operation of the engine.